NDT of Small Defects in Electric Resistance Welds

Dr Neil Hankinson, Sheffield
Dr Rob Dwyer-Joyce, Sheffield 
Dr Bruce Drinkwater, Bristol
Dr Lewis Morgan, BG Technology

on-destructive testing is vital in the maintenance of high pressure gas pipeline. A common and effective practice is to use ultrasound to detect sub-surface defects and flaws in the material. Flaws which are large compared with the ultrasonic wavelength will cause the pulse to be reflected. The reflections of the pulse can be used to spatially map the location of large cracks/inclusions within the material.

 

This project is concerned with the assessment of small defects that are currently invisible to conventional NDT methods. These defects act to scatter (and hence attenuate) an ultrasonic wave. The level of attenuation is dependent on the size, shape, distribution, and nature of the defect.

 

It is frequently difficult to separate these factors to precisely predict defect presence. It is therefore essential to know more about the expected defect population before ultrasonic measurements can be interpreted.

In this work we are concerned with electric resistance welded (ERW) gas pipe. Steel plate is formed into a cylinder, the seam is prepared and induction welded.  Currently, pipes containing several different weld treatments, supplied by Advantica Technologies Ltd., are under investigation. The samples have been subjected to the same loading history yet some have large cracks penetrating through the weld whilst the rest remain intact.  The failure is due to the presence of oxides within the weld. The intention of the work is to refine current ultrasonic techniques for application to micro defects produced in electric resistance welding.

Sponsors

We are grateful to Advantica Technologies Ltd. and the EPSRC for the sponsorship of this work.

Publications:

  1. Hankinson, N., Dwyer-Joyce, R.S., and Drinkwater, B.W., (2001), Observations of Rough Crack face Contact under Load, Proc. 27th Leeds-Lyon Symposium on Tribology, Elsevier, pp. 819-827, (ISBN 0-444-50581-4).
  2. Hankinson, N., Dwyer-Joyce, R.S., Drinkwater, B.W. & Morgan, L., 2001, "Ultrasonic Reflection From Cracks in Electric Resistance Welds in Gas Pipes", Proc. 9th Int. Gas Res. Conf., Amsterdam.